This invention relates generally to furnaces for supplying heat to processing units used in the petroleum refining, chemical processing and other areas; and more particularly the invention concerns an improved, less complex and less expensive furnace having only one section, i.e., combining into one section the functions of the prior two section (radiant and convection) furnace.
Industrial furnaces are involved in most of the above mentioned industrial processes. Such a furnace is normally required to supply heat to the process. It can be direct or indirect heating. For direct heating, a furnace is required; and for indirect heating, a heat transfer medium is used, such as steam, Dowtherm, etc. The heating of a heat-transfer medium also requires a furnace, such as a steam boiler.
A furnace generally has two sections or boxes, namely, a radiant section and a convection section. Both sections contain heating coils where heat is transferred from the hot gases produced by combustion of fuel with air into the process fluid (petroleum, petroleum derivative, chemicals, etc.)
In the radiant section, fuel is burned with combustion air, and heat is transferred by radiation. In the early days when the cost of fuel was less expensive and more abundant, the furnace had only the radiant section. Later, when the cost of fuel became more expensive, the thermal efficiency of the furnace was of great concern. The convection section was added to the radiant section, thus improved the thermal efficiency of the furnace. In such a furnace, the hot flue gas (products of combustion) that leaves the radiant section at elevated temperature enters the convection section where heat is transferred by convection from the hot flue gas to the process. Such a furnace, as currently used and required, is complex and expensive, requiring multiple sets of tubes and supports, therefor for both the radiant and convection sections, and repair and replacement of such tubes, is a highly costly operation.